June 24, 1998
02:00 PM (EDT)

News Release Number: STScI-1998-23

Hubble Space Telescope Helps Find Evidence that Neptune's Largest Moon Is Warming Up

June 24, 1998: Observations obtained by the Hubble telescope and ground-based instruments reveal that Neptune's largest moon, Triton, seems to have heated up significantly since the Voyager spacecraft visited it in 1989.

Even with the warming, no one is likely to plan a summer vacation on Triton, which
is a bit smaller than Earth's moon. Since 1989 Triton's temperature has risen
from about 37 on the absolute (Kelvin) temperature scale (-392 degrees Fahrenheit)
to about 39 Kelvin (-389 degrees Fahrenheit). The scientists are basing a rise
in Triton's surface temperature on the Hubble telescope's detection of an increase
in the moon's atmospheric pressure, which has at least doubled in bulk since the
time of the Voyager encounter. When Triton passed in front of a star known as
"Tr180" in the constellation Sagittarius, Hubble measured the star's gradual decrease
in brightness. The starlight became fainter as it traveled through Triton's thicker
atmosphere, alerting astronomers to changes in the moon's air pressure.